Vortex separator



Oct. 15, 958 T BHR ET AL 3,405,803

VORTEX SEPARATOR Filed Aug. 24, 1964 I N VE NTOKS rHEoDoR l.b/1H? w/L HELM MULLER-RID Fig. 2

United States Patent O 3,405,803 VORTEX SEPARATOR Theodore Bhr and Wilhelm Mller-Rid, Heidenheim,

Germany, assgnors to J. M. Voith G.m.b.H., Heidenheim, Germany Filed Aug. 24, 1964, Ser. No. 391,455 Claims priority, application Austria, Aug. 26, 1963, A 6,812/63 7 Claims. (Cl. 209-211) This invention relates to centrifugal separators or clariiiers, particularly of the vortex type such as are adapted for the separation or clarification of suspensions, pulps, and the like containing in suspension bodies which it is desired to separate according to a predetermined classification.

Vortex separators of this type are particularly useful in the preparation of fibrous pulps in the manufacture of paper and cardboard because such pulps in crude condition contain substantial amounts of heavy particles such as sand and metal and furthermore, contain gases such as air and other particles lighter than the desirable pulp particles, such as fragments of bark.

In this disclosure the term heavy particles means those particles which have a specific gravity higher than that of the desired particles, Whereas the term light particles means those particles which have a specific gravity lighter than the desired particles.

Vortex separators consist, basically, of a tubular vortex chamber which receives uid to be clarified through a tangential inlet at one end, usually at the top. The chamber tapers inwardly in a direction 'away from the inlet, usually in the downward direction, and when fluid is introduced into the separator through the inlet it will move toward the opposite end of the separator, where an outlet is provided and will rotate within the separator at an ever increasing speed so that high centrifugal forces are introduced which drive the heavy particles toward the outer periphery of the separator so that they can be drawn off from the bottom while the lighter particles in the liquid remain therein and can be drawn off from the top of the separator. Such separators, due to the high speed of rotation of the liquid therein, will normally have an axially extending space in the center free of liquids and usually containing gases. These gases are driven oft` from the liquid by the pressure developed in the liquid due to its spiral movement in the separator chamber.

Surrounding the central gas-filled space in the separator is a free liquid surface from which the heavy particles have been centrifuged. The lighter particles will, of course, be contained in the suspension inwardly from the outer portion of the liquid into which the heavy particles have been drawn.

Separators of this type have been proposed with special devices for removing lighter particles or foreign bodies and which would, of course, be disposed toward the center of the separator. Such devices might comprise -a discharge tube extending into the vortex chamber to remove the material from the center portion thereof. Since, however, most of the lighter foreign bodies collect in the vortex circulation that moves toward the discharge tube for the clarified suspension, most of the said lighter particles do not reach the inlet end of the removal device but are carried away with the clarified suspension.

In another type separator the formation of the central gaseous space or core is prevented by supporting a deecting plate in the chamber which shields the vortex chamber from the dirt collecting space at the bottom and upon the upper side of which plate the clarified suspension is diverted inwardly and upwardly to enter a trap opening or discharge tube located slightly above the said plate. Within the tube the trap opening is provided for removing ice lighter foreign bodies. With this arrangement, however, it is extremely difficult to maintain the lighter foreign bodies in an isolated region and the separation of lighter particles with this type of arrangement is quite difiicult.

It has also been suggested to subdivide the vortex separator and to effect the separation of the lighter particles from the clarified suspension in another device. This other device is in the form of a vortex separator with tangential feeding at the lower end, while at the upper end it is provided with a discharge tube having an umbrella-like trap opening for the lighter foreign bodies, and a concentric discharge opening for the clarified suspension, this lastmentioned opening also being shielded from the vortex chamber by the walls of the umbrella-like trap. This construction also embodies a central guide cone along the lighter particles and guided by the conical surface. The friction encountered by the rotating fluids in this arrangement also interferes with the separation of the lighter particles.

Still another arrangement provides the provision of suction openings or outlets in axial alignment at the upper or lower end of a vortex chamber so that the gases which collect in the core can be drawn off by a suction pump. This is effective for removing gases but is ineffective for the important operation of separating light particles from the clarified suspension and is, furthermore, expensive and complex.

It has been found that the pressure in the vortex chamber of a vortex separator varies considerably, depending on the ratio of the gas liberated from the suspension to the amount of gas that is removed by the suction pump. Such pressure changes cause changes in the speed of vortex motion of the fluid in the separator, and this leads to uneven separation of the heavy particles and this can cause undulations and turbulence in the gas core of the chamber. Such separating operations, with the variation in the gas core lead to improper results because they tend to change the level of the paper pulp over the screen of papermaking machine, and this leads to the production of paper of nonuniform thickness.

The aforementioned breathing or change in size of the gas core furthermore greatly hinders the formation of a stable layer of lighter particles in the liquid around the said core, and furthermore makes it extremely difficult to control the suction pump to prevent the carrying awayrby the pump of some of the desired fibrous pulp.

Attempts have been made to eliminate or reduce the aforementioned pulsations and breathing of the central gaseous core in such separators, including the provision of abutment surfaces to support the gaseous core and the provision of conical elements in the core region directed toward the inlet side of the separator. It is also known that such a conical surface could be provided with a recess at the apex to support the gaseous core.

It is still further known with such a separator to have the discharge tube for the desired pulp to extend into tially into the -pulp receptacle. In this arrangement the upper cover of the pulp receptacle carries a conical sur-v face arranged coaxially with the vortex chamber and having a conical apex extending into the pulp receptacle for supporting the gaseous core.

None of the foregoing arrangements, however, have resulted in stabilization of the gaseous core and it is therefore not possible with any of these known vortex separators to keep the layer of lighter lforeign particles surrounding the gaseous core in the form of a stable layer separated from the desired Huid and to divert the layer with the lighter particles to the outside of the separator without losing too much of the desired pulp at the same time. Thus there has not heretofore been any satisfactory arrangement for separating lighter foreign bodies 3 or particles from usable pulp directly within a vortex separator.

With the foregoing in mind the primary object of the present invention is the provision of a vortex separator operable for separating both heavy particles and light particles from a liquid suspension and to accomplish this simultaneously and with a high degree of eiciency.

Another object of this invention is the provision of a separator as referred to above including an arrangement for removing gases under controlled conditions from the gaseous core of the separator.

A still further object of the present invention is the provision of a vortex separator or clarifier of the nature referred to which is readily adjustable or convertible from one separating condition to another whereby the separator becomes readily adaptable to substantially all circumstances.

According to this invention, a separator comprising a substantially tubular vortex chamber, at one end of which there is a tangential inlet opening for the pulp to be clarified, together with a discharge tube for the claried usable pulp, and at the other end a discharge opening for the already separated foreign bodies with specific gravity higher than the -pulp is provided with a second discharge tube dipping into the pulp discharge tube and whose outer diameter is smaller than the inner diameter of the latter while its inlet opening has a diameter which is larger than that of a hollow space which during operation-of the separator will form centrally along the length of the separator and will continue into said second discharge tube.

With a vortex separator of such construction the deficiencies of heretofore known vortex separators are avoided. The instability of the central hollow space or gaseous core inside the vortex current is greatly diminished while the tubes which surround the uppermost portion of the hollow space or gas core, namely the pulp discharge tube and the other discharge tube dipping into the former for removal of the lighter foreign bodies tend to keep the hollow space or gas core in central position. Since the lower portion of the hollow space or gas core remains coaxial with the tapered lower end of the vortex chamber from which the heavier foreign bodies are discharged, the instability and the breathing of the gas core that is observed in the known separators is greatly diminished.

Due to the greater stability of the gas core, it follows that the free surface layer of the liquid moving in a spiral path in the separator around the core will also be stabilized and this will, in turn, provide for a substantial stable layer around the gas core in which the lighter particles to be removed migrate.

At least in the neighborhood of the inlet end of the discharge tube for lighter foreign bodies and of the discharge opening for heavier foreign bodies the hollow space or gas core remains centralized with a uniform round cross section. The inlet end of the discharge tube for lighter foreign particles is therefore provided with an inside diameter equal to the diameter of the liquid layer which immediately surrounds the hollow space or gas core and the lighter foreignbodies. The fibrous content of the liquid that contains these lighter foreign bodies is so small that recovery of the fibers is not necessary.

An especially advantageous form of vortex chamber with the pulp discharge tube inserted through the inlet end of the chamber results if the discharge tube for the lighter foreign bodies is also supported by the inlet side of the vortex chamber. By such construction parts it is possible to avoid construction which would interfere with the formation of coaxial hollow cylinder spaces or gas cores.

Another novel feature of this invention is that the diameter of the pulp discharge tube remains constant or diminishes in the direction of ow from its inlet end to the inlet end of the discharge tube for lighter foreign bodies.

With such constructions, the hollow space or gas core is kept in centralized position and a disruption thereof at the end which enters the pulp discharge tube is avoided. Such disruption of the hollow space or gas core, as has been observed in cases where the cross section increases in the direction of ow, would hinder the separation of the lighter foreign bodies and the gases from the suspension.

In order to insure the separation of lighter foreign bodies at the boundary surface of the gas core, the inlet end of the discharge tube for lighter foreign bodies is spaced from the inlet end of the pulp discharge tube and toward its discharge end by at least twice the diameter of the latter tube, measured along the axis of the Vortex chamber. The lighter foreign bodies will then have sufficient time and length of path to migrate through the fluid transversely to its direction of travel.

Another feature of this invention is that the distance the tube for discharging the lighter foreign bodies dips below the level of the pulp outlet opening which is nearest the discharge opening for the heavier foreign bodies, is at least twice the inside diameter of the inlet end of said tube.

The gases which collect in the gaseous core in a vortex separator of this construction are generally removed together with the lighter foreign bodies. It is, however, possible to separate the gases which collect in the hollow space from the lighter foreign bodies in the separator itself and to discharge them separately. For this purpose a third tube is positioned with its inlet opening centered in the discharge tube for the lighter foreign bodies to serve as a gas outlet tube whose inlet opening has about the same diameter as the gas core and which is spaced in the axial direction from the inlet opening of the radially closest discharge tube (generally the discharge tube for the lighter foreign bodies), toward the outlet end of the latter, by at least twice the diameter of the inlet end of the latter. With such an arrangement of the inlet opening of the gas outlet tube, the exact position of the gas core and its circular cylindrical cross section in the region of the inlet opening of the gas outlet tube and of the receiving end of the discharge tube for lighter foreign bodies will be ensured, with an eicient separation of the gases from the lighter foreign bodies.

If additional coaxial layers of liquid are to be separated from around the air core, it would, of course, be possible to provide additional discharge tubes coaxial with one another similar to those for the discharge of pulp, lighter foreign bodies and gas. The inlet openings of successive tubes would then be spaced axially from each other in the manner described above. The inlet end of the tube of largest diameter must always be closer to the discharge opening for the heavier bodies than the receiving end of the next smaller discharge tube and spaced longitudinally by at least twice its own diameter from the latter.

Another feature of this invention is to have the pressure in the gas outlet tube above atmospheric. In that manner the breathing of the gas core will be eliminated and its movements will be substantially completely quieted. As a result the separation of the heavier, as well as the lighter, foreign bodies and the formation thereof into layers will be more nearly complete. The pressure in the vortex separator and especially at the discharge openings will be increased to above atmospheric and, in that manner, vacuum pumps and the like can be dispensed with.

In order to reach the same speeds and the same outputs with vortex separators operated above atmospheric pressure as are reached with separators operated by the application of suction to the gas core, the pressure in the crude suspension and the performance of the pressurizing pump for the suspension to be clarified need to be increased only slightly. The additional cost thereof is more than compensated by the smaller floor space required by pressurized separators which do not need the additional conduits and sources of power that are required for operating the vacuum pumps.

Practical tests have shown that a positive pressure of at least five meters of water gives satisfactory results. It has been found that with a positive pressure in the gas outlet tube of ten meters of water the residual gas content of pulp from diiiicultly degasiable suspensions is reduced to 8%, and of pulp from easily degasiable suspensions to 1% of the gas content of the crude suspension.

Another feature of this invention is the presence of an adjustable throttle valve in the gas outlet tube whereby the pressure in that tube and hence the pressure relations in the separator can be adjusted to the most favorable values for the particular suspension being treated. If desired, the discharge tube for the lighter foreign bodies and the pulp delivery tube can also be provided with throttle valves.

Another feature of this invention is to have the gas discharge tube adjustable in the axial direction so that its inlet end can be given the most favorable position, relative to the inlet end of the tube which discharges the lighter foreign bodies, for gas release and stabilization.

Instead of a separate gas release tube there can also be provided a transverse disc adjustable in the axial direction inside the discharge tube for the lighter foreign bodies, to be used when a separate removal of the gas is not necessary or when the gas which collects along the center of the vortex chamber is released together with the heavier foreign bodies through the same outlet opening of the vortex chamber, the disc being provided with openings for the passage of the lighter foreign bodies. Instead of such openings, a gap can be provided between the outer periphery of this disc and the inner wall of the discharge tube to permit the passage of the lighter foreign bodies.

Another feature of this invention is to provide the inner ends of the pulp delivery tube, the discharge tube for the lighter foreign bodies and if present, also the gas release tube, namely the ends which are directed toward the vortex chamber, with sharp edges. These will not only effect a sharper separation of the adjacent layers from each other, but will also prevent the formation of ring-shaped vortices at the free end of the tubes which would travel along with the Huid current and disturb the air core along the center which will be rendered less stable which would prevent the uniform separation of foreign bodies with consequent loss of pulp.

The invention is further disclosed in the drawing in the various figures of which like reference characters are used to designate the same or corresponding parts.

FIGURE l shows schematically a longitudinal section through a vortex separator constructed according to this invention;

FIGURE 2 shows on a larger scale the upper portion of a vortex separator of modified construction;

FIGURE 3 shows a variation of the construction shown in FIGURE 2, and

FIGURE 4 shows on a still larger scale a across section on line IV-IV of FIGURE 3 showing another variation.

The vertical vortex separator of FIGURE 1 comprises a tubular vortex chamber 1 provided at its upper inlet end 2a with a tangential inlet conduit 2 for the crude suspension to be clarified. The lower end of the vortex chamber is conically tapered to form an outlet opening 3 for the removal of the separated heavier foreign bodies 4 which have gravitated downwardly along the inner wall of the conical portion.

The vortical motion inside the vortex chamber 1 and at its lower end where the heavier foreign bodies are to be removed has been shown on the drawing by arrows. Through the cover member 5 which closes the upper end of the vortex chamber the pulp delivery tube 6 extends coaxially into the cylindrical upper portion of the chamber 1 and across the axial extent of the inlet opening 2 for the crude suspension to be clarified so that the inlet opening 7 of the pulp delivery tube 6 will be closer than the inlet opening 2 to the outlet opening 3 at the lower end of the vortex chamber. To the upper end of the pulp delivery tube 6 which is closed by an end wall 8, a pulp discharge conduit 9 is connected tangentially through which the pulp is delivered to its destination.

Through the end wall 8 a discharge tube 10 is extended coaxially into the pulp delivery tube 6 for the removal of the lighter foreign bodies. The distance 13a of the inlet end of the discharge tube 10 from that end of the discharge opening 9a of the pulp delivery tube 6 which is nearest the discharge opening 3 for the heavier foreign bodies should be at least twice the inside diameter of the inlet end 13 of the discharge tube 10. The inside and outside diameters of the tube 10 are considerably smaller than the inside diameter of the pulp delivery tube y6 so that suicient space will remain between the outer surface of discharge tube 10 and the inner surface of pulp delivery tube 6 for passage of the pulp.

The tube 6 is cylindrical between its inlet end 7 and the receiving end 13 of tube 10 for the lighter foreign particles, so that its cross section throughout the distance remains the same, although it could become smaller in the upward direction of ow. The inside diameter of the discharge tube 10, or at least of its receiving end 13, must however be large enough to receive not only the central gas core but also the fluid layer 12 composed of the lighter foreign bodies so that these, together with the liberated gases can be separated from the pulp and delivered to the discharge conduit 14.

The discharge tube 10 can be made interchangeable so that discharge tubes 10 with inlet openings 13 of various diameters can be used with the same vortex separator. In that manner the diameter of the inlet opening 13 can be fitted to the outer diameter of the layer 12 to be discharged. Instead of making the entire discharge tube 10 interchangeable, it is also possible to make only the end portion of it with the receiving end 13 interchangeable.

The vortex separator construction shown in FIGURE 2 differs from that of FIGURE 1 especially in the provision of a gas outlet tube 15 coaxial with the discharge tube 10 and longitudinally adjustable therein which not only permits the accumulated gas in the core 11 to escape but also stabilizes the core. The inlet opening 16 of the gas discharge tube 15 has about the same diameter as the gas core 11. If necessary the diameter of the inlet opening 16 can be varied by providing interchangeable tube 15 with different inlet diameters, or only the lower portions of such tubes could be made interchangeable to provide end openings of different diameters. The gas outlet tube 15 is supported for longitudinal adjustment in the upper end 22 of the tube 10 which is equipped with a stuing box 17 and stop means 18 to hold the tube 10 in any adjusted position.

The inlet end 16 of the gas inlet tube 15 is spaced from the trap opening 13 of the tube 10 for lighter foreign bodies in the axial direction toward the outlet opening 20 by a distance equal to about twice the inside diameter of the trap opening 13. The cross section of the pulp tube 6 between its inlet opening 7 and the inlet opening 13 of the tube 10 for lighter foreign bodies, and also the cross section of this discharge tube 10 between its trap opening 13 and the inlet opening 16 of the gas -discharge tube 15, remain constant or decrease in the direction of ow. The gas discharge tube 15 is also provided with an adjustable throttle valve 19 to regulate the pressure in the gas core 11 so as to stabilize the latter and thereby produce better separation of the lighter and heavier foreign bodies.

In order to effect sharp separation of the various coaxial layers in the vortical fluid, the ends of the pulp tube 6 of the discharge tube 10 for lighter foreign bodies and of the gas discharge tube 15 are provided with sharp edges.

The inside diameter of the trap opening 13 of the tube 10 is greater than the outside diameter of the gas outlet tube 15 by an amount equal to double the thickness of the uid layer 12 which contains the lighter foreign bodies. In order to fit this inside diameter of the opening 13 to the outside diameter of the layer 12, the discharge tube or at least its inner end is made interchangeable. In order to permit such interchangeability, the tube 10 and the collar 21 at the upper end of the pulp tube 6 are screw-threaded. This screw thread can at times also be used to adjust the distance by which the discharge tube 10 extends into the pulp tube 6.

In the construction shown in FIGURE 3, the discharge tube 10 for the lighter foreign bodies has in it an axially adjustable transverse disc 23 to provide end support for the gas core 11 which is then kept in central position by the discharge tube 10. The axial position of the disc 23 can be adjusted and maintained by means of the stem 25 so as to control on the one hand the amount of gas which in this case escapes together with the heavier particles through the lower discharge opening 3 (see FIG- URE 1), and on the other hand the movement of the lighter foreign bodies and liquid carried along therewith in the discharge tube 10, there being a clearance space 24 between the outer periphery of the disc 23 and the inner surface of the tube 10.

FIGURE 4 shows a modified form 23 of this disc which is guided along the inner wall of tube 10 by projections 26, between which there are open spaces 27 through which lighter foreign particles can escape.

It will be understood that this invention is susceptible to modification in order to adapt it to different usages and conditions; and accordingly, it is desired to comprehend such modifications within this invention as may fall within the scope of the appended claims.

What is claimed is:

1. A vortex separator for clarifying a suspension containing particles both heavier and lighter than the particles to be retained in the clarified suspension comprising; a Igenerally tubular vortex chamber, a tangential inlet opening for the suspension to be clarified at one end of the vortex chamber, a discharge opening for the heavier particles separated out from the suspension and located at the other end of the vortex chamber, said vortex chamber including a central gas core when the suspension is passing through the vortex chamber, a first discharge tube for the clarified suspension extending axially into the vortex chamber from the inlet end thereof so as to have its inlet opening at a point beyond the inlet opening of the vortex chamber and having a discharge opening in its outer end, a second discharge tube extending axially into the first discharge tube from the outer end of the first discharge tube but terminating short of the innermost end of said first discharge tube so as to have its inlet opening at a point ybeyond the discharge opening of the first discharge tube, the inlet end of said second discharge tube being spaced from the inlet end of said -rst discharge tube towards its discharge end a distance which is at least twice the inlet `diameter of said first discharge tube, a third discharge tube extending into said second discharge tube from its outer end and terminating short of the inner end of said second discharge tube, said third discharge tube having a diameter substantially smaller than the diameter of said second discharge tube, and the inlet end of said third discharge tube being spaced from the inlet end of said second discharge tube towards its discharge end a distance which is at least twice the inside diameter of said second discharge tube, the inlet end of said second discharge tube being spaced from the discharge opening of said first discharge tube a distance equal to at least twice the diameter of said second discharge tube.

2. The arrangement according to claim 1 which in- 8 cludes means for maintaining the gas in said gas core at a positive pressure on the order of about 5 meters of water column.

3. The arrangement according to claim 2 in which said means comprises an adjustable throttle valve located in said third discharge tube.

4. The arrangement according to claim 1 in which said third discharge tube is supported on said second discharge tube for axial adjustability therein.

5. A vortex separator according to claim 1 in which said first, second and third discharge tubes have their inlet ends sharpened to provide minimum obstruction to suspension passing the said tubes.

6. A vortex separator for clarifying a suspension containing particles both heavier and lighter than the particles to be retained in the clarified suspension comprising; a generally tubular vortex chamber, a tangential inlet opening for the suspension to be clarified at one end of the vortex chamber, a discharge opening for the heavier particles separated out from the suspension and located at the other end of the vortex chamber, said vortex chamber including a central -gas core when the suspension is passing through the vortex chamber, a first discharge tube for the clarified suspension extending axially into the vortex chamber from the inlet end thereof so as to have its inlet opening at a point beyond the inlet opening of the vortex chamber and having a discharge opening in its outer end, a second discharge tube extending axially into the first discharge tube from the outer end of the first discharge tube but terminating short of the innermost end of said first discharge tube so as to have its inlet opening at a point beyond the discharge opening of the first discharge tube, the inlet end of said second discharge tube being spaced from the inlet end of said lfirst discharge tube towards its discharge end a distance which is at least twice the inlet diameter of said first discharge tube, said inlet end of said second discharge tube being spaced from the discharge end of said first discharge tube a distance equal to -at least twice the diameter of said second discharge tube, a disc in said second discharge tube between its inlet opening and its discharge opening and adjustable axially therein for supporting the gas core in said separator, and passage means for permitting suspension entering the inlet opening of said second discharge tube to pass said disc and thereby move on to the discharge opening of said second discharge. tube.

7. The arrangement according to claim 6 in which said disc has peripheral notches therein forming the said passage means.

References Cited UNITED STATES PATENTS 2,098,608 11/1937 Berges 209-211 X 2,375,826 5/ 1945 Scott 209-211 2,379,411' 7/ 1945 Berges 209-211 2,724,503 11/ 1955 Fontein 209-211 2,756,878 7/ 1956 HerkenhOff 209-211 2,816,490 12/1957 Boadway 209-211 X 2,819,795 1/ 1958 Fontein 209-211 2,923,151 2/ 1960 Engle 209-211 X 2,981,413 4/ 1961 Fitch 209-211 X 3,105,044 9/ 1963 Troland 209-211 X FOREIGN PATENTS 1,314,386 12/1962 France.

FRANK W. LUTTER, Primary Examiner. 

1. A VORTEX SEPARATOR FOR CLARIFYING A SUSPENSION CONTAINING PARTICLES BOTH HEAVIER AND LIGHTER THAN THE PARTICLES TO BE RETAINED IN THE CLARIFIED SUSPENSION COMPRISING; A GENERALLY TUBULAR VORTEX CHAMBER, A TANGENTIAL INLET OPENING FOR THE SUSPENSION TO BE CLARIFIED AT ONE END OF THE VORTEX CHAMBER, A DISCHARGE OPENING FOR THE HEAVIER PARTICLES SEPARATED OUT FROM THE SUSPENSION AND LOCATED AT THE OTHER END OF THE VORTEX CHAMBE, SAID VORTEX CHAMBER INCLUDING A CENTRAL GAS CORE WHEN THE SUSPENSION IS PASSING THROUGH THE VORTEX CHAMBER, A FIRST DISCHARGE TUBE FOR THE CLARIFIED SUSPENSION, EXTENDING AXIALLY INTO THE VORTEX CHAMBER FROM THE INLET END THEREOF SO AS TO HAVE ITS INLET OPENING AT A POINT BEYOND THE INLET OPENING OF THE VORTEX CHAMBER AND HAVING A DISCHARGE OPENING IN ITS OUTER END, A SECOND DISCHARGE TUBE EXTENDING AXIALLY INTO THE FIRST DISCHARGE TUBE FROM THE OUTER END OF THE FIRST DISCHARGE TUBE BUT TERMINATING SHORT OF THE INNERMOST END OF SAID FIRST DISCHARGE TUBE SO AS TO HAVE ITS INLET OPENING AT A POINT BEYOND THE DISCHARGE OPENING OF THE FIRST DISCHARGE TUBE, THE INLET END OF SAID SEC- 